Field of the Invention and Related Art Statement
The present invention relates to an ultrasonic diagnostic apparatus having an ultrasonic observation system to obtain an ultrasonic tomographic image of a portion of a body of patient with the aid of a ultrasonic waves and an optical observation system to obtain an optical image of the portion.
Such ultrasonic endoscope diagnostic apparatuses having the ultrasonic observation system and the optical observation system are widely used and disclosed in publications such as U.S. Pat. No. 4,605,009 and German Patent laid-open Publication No. 3336803. In the former publication, the apparatus is constructed such that an optical viewing field of the optical system and an ultrasonic observation field are made consistent with each other in a fixed manner, so that ultrasonic observation and optical observation can be effected simultaneously, while the positional relationship between the optical image and the ultrasonic tomographic image is maintained. In the later publication, the apparatus is constructed such that light exiting windows ar arranged in both sides of an ultrasonic vibrating element of linear scan type to make it possible for the endoscope arranged at the opposite side of the ultrasonic vibrating element to detect the light emitted from the windows, so that an operator can recognize the portion where the ultrasonic wave is emitted.
However, in these conventional ultrasonic endoscope diagnostic apparatus, it is sometimes difficult for the operator to recognize the positional relationship between the ultrasonic tomographic image and the optical image so that the operator cannot operate the endoscope in an effective manner. Particularly, in an ultrasonic endoscope diagnostic apparatus of radial scanning type, in order to obtain an ultrasonic tomographic image in a standard position, it is often required to rotate the ultrasonic tomographic image displayed on the monitor screen. When the ultrasonic tomographic image is rotated on the screen, the given positional relationship between the ultrasonic tomographic image and the optical image no longer exists so that it becomes difficult to recognize the direction of the optical image with respect to the ultrasonic tomographic image.
In Japanese Laid-open Patent Publication No. 60-227740 and Japanese Laid-open Utility Model Publication No. 61-57908, there are suggested known ultrasonic endoscope diagnostic apparatuses of radial scanning type. In these apparatuses, the ultrasonic vibrating element is rotatably arranged in the distal end portion of the insertion section of the apparatus and is connected to a distal end of a flexible shaft which is extended in the insertion section to transmit a rotation of a motor provided in the operating section of the apparatus to the ultrasonic vibrating element. In these apparatuses, a device for detecting the rotational position of the ultrasonic vibrating element arranged in the distal end portion of the insertion section of the apparatus is arranged in the operating section of the proximal end of the apparatus in order to make the insertion section small and short. However, when the insertion section is inserted in a cavity of a living body, the insertion section is bent along the curvature of the cavity. Further, in order to observe the desired portion of the cavity, the operator sometimes bend a bending section of the insertion section by operating angle knobs arranged in the operating section of the proximal end portion of the apparatus. In this case, a resistance against a rotational movement of the flexible shaft is increased and the flexible shaft becomes twisted, so that there would occur a deviation between the rotational phase of the ultrasonic vibrating element detected by a rotational phase detecting device such as an encoder and the actual rotational phase thereof. Therefore, the predetermined positional relationship between the ultrasonic tomographic image and the optical image would be altered.
In order to compensate for the deviation of the optical image with respect to the ultrasonic tomographic image, the insertion section is rotated in the cavity. However rotating the insertion section in the cavity is not undesirable not only because of the decrease in the durability of the insertion section but also because of the danger of transforation in the cavity.
On the other hand, an ultrasonic endoscope diagnostic apparatus having a miniature ultrasonic probe has been suggested. The apparatus is constructed such, that the miniature ultrasonic probe is capable of being inserted in a forceps channel which is provided in the insertion section of the apparatus, and the, distal end of the miniature ultrasonic probe is taken off from an opening arranged in the top end section of the insertion section to scan the portion of the body with the aid of ultrasonic waves. Such apparatus also has the same problem described above, so that, there would occur a deviation of the positional relationship between the ultrasonic tomographic image and the optical image.